Update Twitter card tags for homepage

According to https://dev.twitter.com/docs/cards/types/summary-card

index.html

@@ -6,6 +6,9 @@
 		<meta name="description" content="Helping you select an MV* framework - Todo apps for Backbone.js, Ember.js, AngularJS, Spine and many more">
 		<meta name="viewport" content="width=device-width,initial-scale=1">
 		<meta name="twitter:card" content="summary">
+		<meta name="twitter:title" content="TodoMVC">
+		<meta name="twitter:description" content="Helping you select an MV* framework - Todo apps for Backbone.js, Ember.js, AngularJS and many more">
+		<meta name="twitter:image" content="https://raw.githubusercontent.com/tastejs/todomvc/gh-pages/site-assets/screenshot.png">
 		<meta property="og:url" content="http://todomvc.com">
 		<meta property="og:title" content="TodoMVC">
 		<meta property="og:image" content="https://raw.github.com/tastejs/todomvc/gh-pages/site-assets/screenshot.png">